aptly
Debian repository management tool
...Take and update mirrors of any Debian/Ubuntu remote repository. At any point in time, take a snapshot of the mirror to fix the current set of packages. Merge two or more snapshots into one snapshot: e.g. merge wheezy and wheezy-updates. Manage your own repositories of packages, merge them with official and publish the result. Any snapshot could be published back as a repository (only HTTP server is required). Is the new package version available in backports? Pull only a single package with dependencies from backports into a snapshot of the stable repository.